This K22 Faculty Transition Award is intended to provide the initial support for the independent research program of the candidate, Scott A. Weed. Dr. Weed was appointed to a tenure track position at the University of Colorado Health Sciences Center following completion of his postdoctoral training. He is continuing his studies on the cytoskeletal and signaling protein, cortactin. Dr. Weed's appointment in the Department of Basic Sciences and Oral Research in the School of Dentistry allows him access to all forms of major modern instrumentation for his studies and provides an intellectually stimulating environment. Dr. Weed and his laboratory are involved in a variety of research group meetings involving all Departmental laboratories, he has access to all members of the School of Medicine research community at UCHSC through a joint appointment. His long-term goals involve further elucidation of the role of cortactin and associated proteins in lamellipodia function as it pertains to normal cell signal transduction and motility, and how this protein is malregulated in oral cancer. This proposal specifically addresses the function of cortactin in tyrosine kinase-based cell signaling events. Cortactin is a substrate for Src and is overexpressed in 30 percent of head and neck squamous cell carcinomas (HNSCCs). Based on his preliminary data, it is hypothesized that tyrosine phosphorylation of cortactin involves multiple signaling pathways including in part activation of the Rho GTPases, Rac and Cdc 42. The studies described here will use biochemical and cell biological analysis of fibroblast cell lines to explore the hypothesis that tyrosine phosphorylation of cortactin is central to the assembly of signaling complexes important for cortical actin assembly and motility. In AIM 1 he will address if cortactin binding to Src activates Src kinase activity, if Rac-induced Src translocation is required for compartmentalization with cortactin in lamellipodia, and to identify proteins interacting with phosphotyrosine residues. AIM2 will examine the role cortactin plays in ACK phosphorylation events by determining if cortactin is an ACK substrate, if ACK-mediated cortactin phosphorylation effects the actin cytoskeleton, and if phosphorylation of cortactin by ACK is involved in Cdc42-mediated cell motility. AIM3 will examine the role of the EGF receptor in cortactin tyrosine phosphorylation by determining the kinases involved in EGFR-mediated cortactin phosphorylation, the role cortactin plays in EGF phosphorylation events, and the identity and function of a l25kDa phosphoprotein complexed with cortactin following EGFR activation.